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Show 1890.] OF THE FAMILY BUTHIDCE. 115 indeed, there are some grounds for thinking that this may have taken place in the case of Grosphus and of Rhoptrurus; for the former appears to connect Lepreus with Buthus, and the latter Lsometrus whh Buthus ; or, in other words, Buthus appears to have arisen from Lepreus by way of Grosphus and from lsometrus by way of Rhoptrurus, that is from two independent sources. And if anyone likes to believe that this has taken place, it is difficult to see how the idea can be shown to be wrong. Of course an alternative hypothesis, namely, that Grosphus is the ancestor of both Buthus and Lepreus, at once suggests itself ; but in that case it is hard to see why Lepreus should have lost the two mandibular teeth, which must surely be of considerable service in the battle for life. Moreover, when we reflect that Ljepreus agrees with almost all the Scorpionidee (including provisionally Vejovis and Botlmurus) in the absence of these teeth, it is hard to believe that it is not a character which has been transmitted to Lepreus from some unknown member of this family. In that case we must, it seems to me, account for the resemblance between Grosphus and Lepreus on the hypothesis that the latter is the ancestor of the former, unless, indeed, we consider that it is the result of what, for want of a better term, may be called accident. However, from whichever side the question be approached, some obstacle presents itself which our knowledge of the affinities of the genera is at present too limited to surmount. For a variety of reasons, however, it seems to me to be perhaps well to regard provisionally Lepreus and Uro-plectes as derived from Grosphus; for undoubtedly in most respects these two genera depart widely from a plan which is common to all the others. With the exception of these two and of Butheolus, a genus hard to locate, the accompanying pedigree (see p. 128) appears to me to represent fairly well the mutual relationship of the genera and subgenera here recognized. But it must be regarded as merely tentative and in no way as expressing a final opinion. Considering the Scorpionidee as a whole and the Buthidse as a whole, and noting what characters are common to both and what are the average characters of the least specialized of the genera of Buthidse, we are able to form some opinion as to the characters of the immediate ancestor of the Buthidae, or, in other words, to discover the common plan from which all the modifications of the various genera can be derived. By this means it may be inferred that in this hypothetical ancestral form the sternum was triangular ; the movable digit of the cheli-cerse was furnished with three teeth above and two below (not counting the terminal fang), the immovable with a single row of teeth ; the armature of the digits of the chelse was composed of a number of oblique, parallel, slightly overlapping rows of denticles; there were two median eyes, and three lateral eyes on each side ; the cephalothorax was granular, but not carinate ; the tergites were granular and furnished with a median keel, the last, in addition, bearing two lateral keels; the sternites were smooth and anteriorly bisulcate, the last only being furnished with two or four keels; the tail was keeled throughout, and there was probably a spine beneath the aculeus |
